It is known that such devices expand high pressure steam to lower pressure steam and thereby generate mechanical or electrical energy.
During operation the inlet valve and outlet valve are open and the device is completely under steam.
When the device is stopped, for example because there is no demand for steam or energy or because there are fault conditions, this inlet and outlet valve are closed and steam is confined in the device, more specifically in the space between these two valves that contains the expander.
This confined steam cools to ambient temperature and due to the properties of the steam the pressure in the aforementioned space will fall and a strong vacuum will be created between the inlet valve and the outlet valve.
As a result air can be drawn into the device, for example through the seals in the steam expand or in the valves or other places.
The combination of air and steam condensate in the device creates a highly corrosive environment to which the components of the device and thus the expander are exposed.
This has the disadvantage that the lifetime of these components is drastically reduced.
Moreover, this has detrimental consequences for the reliability of the device.
An additional disadvantage is that corrosion of the expander itself can make the efficiency fall, such that less energy is produced once the machine is started up again.
An additional disadvantage is that the air in the device can also cause problems downstream in the outlet pipe, as corrosion of the pipes and equipment can occur when the unit is started up again, and efficiency loss in the process due to reduced heat transfer in heat exchangers for example.